This relates generally to electronic devices, and, more particularly, to electronic devices with displays.
Electronic devices such as cellular telephones, computers, and other devices contain displays. A display includes an array of pixels for displaying images to a user. Display driver circuitry such as source line driver circuitry may supply data signals to the array of pixels. Gate line driver circuitry in the display driver circuitry can be used to assert a gate line signal on each row of pixels in the display in sequence to load data into the pixels.
A common electrode voltage layer may be used to distribute a common electrode voltage (Vcom) to the pixels in the array. The common electrode voltage may be formed from a transparent conductive film that covers the array of pixels. Due to overlap between the data lines and the common electrode voltage layer, there may be a non-negligible amount of capacitance between the data lines and the common voltage electrode. This capacitance gives rise to capacitive coupling between the data lines and the common electrode voltage layer. During operation of the display, capacitive coupling can lead to undesired ripple in the Vcom voltage.
To avoid excessive Vcom ripple, which can interfere with display operation, displays use Vcom compensation circuitry. A Vcom compensation circuit for a display includes an op-amp based control circuit. A feedback path provides a sample of the current Vcom voltage value from the Vcom electrode to one terminal of the op-amp. A reference Vcom voltage is applied to another terminal of the op-amp. The op-amp circuit supplies a Vcom voltage output to the Vcom electrode that maintains the Vcom electrode at the desired voltage (i.e., the reference voltage).
The effectiveness of conventional Vcom compensation circuitry is limited by the speed with which the op-amp based control circuit can adjust the Vcom electrode voltage. In conventional displays, control circuit response time is limited, which may adversely affect compensation performance.
It would therefore be desirable to be able to provide a display with improved common voltage compensation circuitry.